5-8

Question 1

Define chemical energy.

Answer 1

Arises from the arrangement of atoms and can be released by a chemical reaction.

Question 2

ATP energy helps cells perform the 3 following types of work:

Answer 2

Motor Proteins: The proteins change shape, causing the muscle cells to contract. This contraction provides the mechanical energy needed.

Transport of Ions: ATP enables the transport of ions and other dissolved substances across the membranes of nerve cells, helping them send signals to different body parts.

Production of a Cell’s Large Molecules: ATP drives the production of a cell’s large molecules from smaller molecular building blocks.

Question 3

Please list and explain the types of transport across membranes.

Answer 3

Passive Transport:

1. Diffusion - Movement of molecules across a membrane (down concentration gradient); does not require energy
2. Facilitated Diffusion - Movement of molecules across a membrane (down concentration gradient) aided by specific transport proteins; requires energy
3. Osmosis - Movement of water molecules across a selectively permeable membrane

Active Transport: Movement of molecules across a membrane (against concentration gradient) aided by specific transport proteins; requires energy

Traffic of Large Molecules:
1. Exocytosis - Proteins exit the cell from transport vesicles that fuse with the plasma membrane, spilling the contents outside of the cell.
2. Endocytosis - A cell takes in materials by vesicles that bud inward.
A. Phagocytosis: Cellular “eating”; a cell engulfs a particle and packages it within a food vacuole.
B. Pinocytosis: Cellular “drinking”; a cell “gulps” droplets of fluids into vesicles.
C. Receptor-mediated Endocytosis: The binding of certain external molecules to specific receptor proteins built into the plasma membrane.

Question 4

Please list and explain the 3 different types of solutions.

Answer 4

1. Isotonic:
   - Has an equal concentration of solute as the cell
   - Water molecules will move in and out of cell at same rate
2. Hypotonic:
   - Has a lower solute concentration of solute to the cell
   - Water molecules will move into the cell at a higher rate
3. Hypertonic:
   - Has a higher solute concentration of solute to the cell
   - Water molecules will move out of the cell at a higher rate

Question 5

What is osmoregulation?

Answer 5

The control of water balance (gain or loss of water and dissolved solutes in an organism)

Question 6

Compare photosynthesis and respiration.

Answer 6

Photosynthesis: The energy of sunlight is converted to the chemical energy of sugars and other organic molecules. Requires the input of carbon dioxide and water and produces oxygen gas as a waste product.

Respiration: Cellular respiration requires a cell to exchange two gases with its surroundings. The cell takes in oxygen in the form of the gas O2. It gets rid of waste in the form of the gas carbon dioxide. Respiration, or breathing, results in the exchange of these same gases between your blood and the outside air.

Question 7

Compare autotrophs and heterotrophs.

Answer 7

Autotrophs: (“Self-feeders”) Organisms that make all their own organic matter from nutrients that are entirely inorganic: They take carbon dioxide from air or water/minerals from soil.

Heterotrophs: (“Other-feeders”) Organisms that cannot make organic molecules from inorganic ones. Humans and other animals.

Question 8

Compare producers and consumers.

Answer 8

Producers: Plants and other autotrophs.

Consumers: Heterotrophs (obtain food by eating plants) or other animals that eat plants.

Question 9

Compare aerobic processes and anaerobic processes.

Answer 9

Aerobic process: Containing or requiring molecular oxygen (O2).

Anaerobic process: (“Without oxygen”) Lacking or not requiring molecular oxygen (O2).

Question 10

Compare the reactants and products of photosynthesis and cellular respiration.

Answer 10

Photosynthesis: Carbon Dioxide (6 CO2) + Water (6 H2O) = Sugar (Glucose) C6H12O6 + Oxygen (6 O2)

Cellular Respiration: Sugar (Glucose) C6H12O6 + Oxygen (6 O2) = Carbon Dioxide (6 CO2) + Water (6 H2O) + approx. 32 ATP + heat

Question 11

What are the roles of NADH and FADH2?

Answer 11

NADH and FADH2 are generated during glycolysis and the citric acid cycle and are electron carriers involved in cellular respiration and photosynthesis. They carry electrons from glucose and other fuel molecules and deposit them at the top of an electron transport chain.

Question 12

Please fully explain how the electron transport chain drives production of ATP.

Answer 12

During cellular respiration, the electrons gathered from food molecules gradually “fall”, losing energy at each step. In this way, cellular respiration unlocks chemical energy in small amounts, that cells can put to productive use.

Electrons are transferred from glucose in food molecules to NAD+. This electron transfer converts NAD+ to NADH. Then NADH releases two electrons that enter an electron transport chain, a series of electron carrier molecules. This chain is like a bucket brigade, with each molecule passing an electron to the next molecule. With each exchange, the electron gives up a bit of energy. This downward cascade releases energy from the electron and uses it to make ATP.

Question 13

Please list the location, inputs and outputs and energy yield for each stage of cellular respiration.

Answer 13

Glycolysis: Cytoplasm; Glucose, ATP, NAD+; Pyruvic Acid, ATP, NADH; 2 ATP
(prep) Citric Acid Cycle: Mitochondria; Pyruvic Acid; Acetyl CoA; 0 ATP
(cycle) Citric Acid Cycle: Mitochondria; Acetic acid, ADP + P, NAD+, FAD; CO2, ATP, NADH, FADH2; 2 ATP
Electron Transport Chain: Mitochondria; NADH, H+, ADP, FADH2, O2; NAD+, ATP, FAD, H2O; 32 ATP

Question 14

Please list the product outputs for NADH, FADH2, CO2, H20, and ATP for each stage of cellular respiration.

Answer 14

Glycolysis: 2 NADH, 0 FADH2, 0 CO2, 0 H20, 2 ATP
Citric Acid Cycle: 3 NADH, 1 FADH2, 2 CO2, 0 H20, 2 ATP
Electron Transport Chain: 0 NADH, 0 FADH2, 0 CO2, 2 H20, 32 ATP
TOTAL: 5 NADH, 1 FADH2, 2 CO2, 2 H20, 36 ATP

Question 15

What is the name of the process when organisms produce ATP in anaerobic environments? How does this process work?

Answer 15

Although we must breathe to stay alive, some of our cells can work for short periods without oxygen. This anaerobic (“without oxygen”) harvest of food energy is called fermentation.

Question 16

Please provide 2 examples of organisms that produce ATP in anaerobic environments. What are the waste products for each of these examples?

Answer 16

Fermentation in Human Muscle Cells
As muscles work, they require a constant supply of ATP, which is generated by cellular respiration. But under strenuous conditions, muscles can spend ATP faster than the bloodstream can deliver O2, when this happens, your muscle cells begin to work anaerobically. After functioning anaerobically for about 15 seconds, muscle cells will begin to generate ATP by the process of fermentation. Fermentation relies on glycolysis, the first stage of cellular respiration. Glycolysis does not require O2 but does produce two ATP molecules for each glucose molecule broken down to pyruvic acid. That isn’t very efficient compared with the 32 or so ATP molecules each glucose molecule generates during cellular respiration, but it can energize muscles for a short burst of activity. However, in such situations, cells will have to consume more glucose fuel per second because so much less ATP per glucose molecule is generated under anaerobic conditions.

To harvest food energy during glycolysis, NAD+ must be present to receive electrons. This is no problem under aerobic conditions because the cell regenerates NAD+ when NADH drops its electron cargo down electron transport chains to O2. However, this recycling of NAD+ cannot occur under anaerobic conditions because there is no O2 to accept the electrons. Instead, NADH disposes of electrons by adding them to the pyruvic acid produced by glycolysis. This restores NAD+ and keeps glycolysis working.

Fermentation in Microorganisms
The two ATP molecules produced per glucose molecule during fermentation are enough to sustain many microorganisms. We have domesticated such microbes to transform milk into cheese, sour cream, and yogurt. These foods owe their sharp or sour flavour mainly to lactic acid. The food industry also uses fermentation to produce soy sauce from soybeans, to pickle cucumbers, olives, and cabbage, and to produce meat products like sausage, pepperoni, and salami.

Yeast, a microscopic fungus, is capable of both cellular respiration and fermentation. When kept in an anaerobic environment, yeast cells ferment sugars and other foods to stay alive. As they do, the yeast produce ethyl alcohol as a waste produce instead of lactic acid. This alcoholic fermentation also releases CO2. We put yeast to work to produce alcoholic beverages like beer and wine using airtight barrels and vats, where the lack of oxygen forces the yeast to ferment glucose into ethanol. Bakers use CO2 bubbles from fermenting yeast to cause bread dough to rise.

Question 17

What is the overall equation of photosynthesis? How does this equation relate to the equation of cellular respiration?

Answer 17

Carbon Dioxide (6 CO2) + Water (6 H2O) -> Light Energy -> Glucose (C6H12O6) + 6 CO2

It’s the reverse of cellular respiration.

Question 18

Photosynthesis occurs in which organelle? Please draw a picture and explain the structure of this organelle.

Answer 18

Photosynthesis occurs in chloroplasts.

A chloroplast has a double-membrane envelope: the chloroplast’s inner membrane encloses a compartment filled with stroma, a thick fluid. Suspended in the stroma are interconnected membranous sacs called thylakoids. The thylakoids are concentrated in stacks called grana. The chlorophyll molecules that capture light are energy are built into the thylakoid membranes. The structure of a chloroplast—with its stacks of disks—aids its function by providing a large surface area for the reactions of photosynthesis.

Question 19

Please list and explain the 3 main pigments in chloroplasts.

Answer 19

Chlorophyll a:

• Absorbs blue-violet and red light.
• Participates directly in the light reactions.

Chlorophyll b:

• Absorbs blue and orange light.
• Does not participate directly in the light reactions, but conveys absorbed energy to chlorophyll a, which then puts the energy to work in the light reactions.

Carotenoids:

• Absorbs blue-green light.
• (1) The colours of fall foliage are partly because of the yellow-orange light reflected from carotenoids. The decreasing temperatures in autumn cause a decrease in the levels of chlorophyll, allowing the colours of the longer-lasting carotenoids to be seen in fall. (2) Some carotenoids have a protective function: They dissipate excess light energy that would otherwise damage chlorophyll. (3) Some carotenoids are human nutrients: beta-carotene is converted to vitamin A in the body, and lycopene is an antioxidant that is being studied for potential anticancer properties.

Question 20

Please explain why chloroplasts appear green. Why do leaves change colours in the fall?

Answer 20

Their green colour is from chlorophyll, a pigment (light-absorbing molecule) in the chloroplasts that plays a central role in converting solar energy to chemical energy. Chloroplasts also contain a family of yellow-orange pigments called carotenoids, which absorb mainly blue-green light. The decreasing temperatures in autumn cause a decrease in the levels of chlorophyll, allowing the colours of the longer-lasting carotenoids to be seen in all their fall glory.

Question 21

Please list the 2 stages of photosynthesis and where each stage occurs in the chloroplast and their inputs and outputs.

Answer 21

The Light Reactions:

• In the thylakoid discs
• Inputs H2O + Light
• Outputs NADPH + ATP

The Calvin Cycle:

• In the stroma
• Inputs NADPH + ATP + C from CO2
• Outputs G3P (Glucose and other organic compounds)

Question 22

Please fully explain how light reactions generate ATP and NADPH. Draw a diagram to help with your explanation.

Answer 22

(1) Photons excite electrons in the chlorophyll of the first photosystem. These photons are then trapped by the primary electron acceptor. This photosystem then replaces the lost electrons by extracting new ones from water. This is the step that releases O2 during photosynthesis.
(2) Energized electrons from the first photosystem pass down an electron transport chain to the second photosystem. The chloroplast uses the energy released by this electron “fall” to make ATP.
(3) The second photosystem transfers its light-excited electrons to NADP+, converting it to NADPH.

Question 23

Please fully explain how the Calvin cycle produces sugar from CO2. Draw a diagram to help with your explanation.

Answer 23

(1) An enzyme adds each CO2 (from air) to a five-carbon sugar called RuBP. The resulting molecule breaks into two three-carbon molecules.
(2) Using energy from ATP and NADPH produced by the light reactions, enzymes convert each three-carbon molecule to the three-carbon sugar G3P.
(3) For every three molecules of CO2 that enter the cycle, the net output is one G3P sugar. The other G3P sugars continue in the cycle.
(4) Using energy from ATP, enzymes rearrange the remaining G3P sugars to regenerate RuBP.

Question 24

What are the 3 main functions of cell division?

Answer 24

Cell Replacement, Growth by Cell Division, Asexual Reproduction

Question 25

Please describe how chromatin condenses into highly packed chromosomes. What are the proteins involved?

Answer 25

Chromosomes are made up of a material called chromatin, fibers composed of roughly equal amounts of DNA and protein molecules. The protein molecules help organize the chromatin and help control the activity of its genes.

Question 26

Please list and explain the 2 main phases in the cell cycle.

Answer 26

Interphase: When the cell is not actually dividing. During interphase, cellular metabolic activity is high, chromosomes and organelles are duplicated, and cell size may increase. Interphase accounts for 90% of the cell cycle.

Mitotic (M) Phase: When mitosis divides the nucleus and distributes its chromosomes to daughter nuclei and cytokinesis divides the cytoplasm, producing two daughter cells.

Mitosis: The division of a single nucleus into two genetically identical daughter nuclei. Cytokinesis: The division of the cytoplasm to form two separate daughter cells. Cytokinesis usually occurs during telophase of mitosis.

Question 27

Please list and explain the 4 main phases in mitosis.

Answer 27

Prophase: During prophase, duplicated chromosomes condense to form structures visible with a light microscope, and the mitotic spindle forms and begins moving the chromosomes toward the center of the cell.

Metaphase: During metaphase, the centromeres of all the cell’s duplicated chromosomes are lined up along the center line of the cell.

Anaphase: Beginning when sister chromatids separate from each other and ending when a complete set of daughter chromosomes has arrived at each of the two poles of the cell.

Telophase: During which daughter nuclei form at the two poles of a cell. Telophase usually occurs together with cytokinesis.

Question 28

Please explain how plants and animals complete cytokinesis differently.

Answer 28

In animal cells, the cytokinesis process is known as cleavage. The first sign of cleavage is the appearance of an indentation called a cleavage furrow. A ring of microfilaments in the cytoplasm just under the plasma membrane contracts, deepening the furrow and pinching the parent cell in two.

In plant cells, cytokinesis occurs differently. Vesicles containing cell wall material collect at the middle of the cell. The vesicles fuse, forming a membranous disk called the cell plate. The cell plate grows outward, accumulating more cell wall material as more vesicles join it. Eventually, the membrane of the cell plate fuses with the plasma membrane, and the cell plate’s contents join the parental cell wall. The result is two daughter cells.

Question 29

Please explain the cell cycle control system. How does this relate to cancer?

Answer 29

For a plant or animal to grow and maintain its tissues normally, it must control the timing of cell division—speeding up, slowing down, or turning the process off or on as needed. The sequential events of the cell cycle are directed by a cell cycle control system that consists of specialized proteins within the cell.

Cancer is a disease of the cell cycle. Cancer cells do not respond normally to the cell cycle control system; they divide excessively and may invade other tissues of the body. Cancer cells may continue to divide until they kill the host; unlike other human cells, they will never cease dividing.

Question 30

What type of cell division do humans use to grow and develop?

What type of cell division do they use to create gametes?

Answer 30

Mitosis, Meiosis.

Question 31

Please briefly explain the life cycle of a human.

Answer 31

1. Two multicellular diploid adults (2n = 46) produce haploid gametes (n = 23) by meiosis. Females produce an egg cell and males produce a sperm cell.
2. Through fertilization, these haploid gametes become a diploid zygote (2n = 46).
3. With mitosis and development, the diploid zygote forms into a multicellular diploid adult (2n = 46) so the process can continue.

Question 32

Please compare the 4 main phases in Mitosis to those in Meiosis I:

Answer 32

Prophase: In mitosis, there are duplicated chromosome (two sister chromatids) and in meiosis, homologous chromosomes come together in pairs (sites of crossing over between homologous nonsister chromatids)

Metaphase: In mitosis, individual chromosomes align at the middle of the cell. In meiosis, homologous pairs align at the middle of the cell.

Anaphase: In mitosis, sister chromatids separate. In meiosis, homologous chromosomes separate; sister chromatids remain attached.

Telophase: In mitosis, there are two haploid daughter cells. In meiosis, there are two haploid daughter cells, but chromosomes are with two sister chromatids.

Question 33

Please explain nondisjunction.

Answer 33

An accident of meiosis or mitosis in which a pair of homologous chromosomes or a pair of sister chromatids fails to separate at anaphase.

Question 34

What is generated during all energy conversions? How does this affect entropy?

Answer 34

All energy transformations generate some heat. Heat is energy in its most disordered, chaotic form, the energy of aimless molecular movement. Entropy is a measure of the amount of disorder, or randomness, in a system. Every time energy is converted from one form to another, entropy increases.

Question 35

Please provide definitions for energy, kinetic energy and potential energy. Please explain the principle of conservation of energy.

Answer 35

Energy: The capacity to cause change.
Kinetic Energy: The energy of motion.
Potential Energy: The energy an object has because of its location or structure.
Conservation of Energy: It is not possible to destroy or create energy.

Question 36

What is generated during all energy conversions? How does this affect entropy?

Answer 36

All energy transformations generate some heat. Heat is energy in its most disordered, chaotic form, the energy of aimless molecular movement. Entropy is a measure of the amount of disorder, or randomness, in a system. Every time energy is converted from one form to another, entropy increases.

Question 37

What are the components of ATP? Which specific component(s) of ATP provide energy for cellular work? How do the chemical characteristics of these components contribute to the potential energy of ATP? (Hint: ATP is like a compressed spring)

Answer 37

ATP consists of an organic molecule called adenosine plus a tail of three phosphate groups. The triphosphate tail is the part that provides energy for cellular work. Each phosphate group is negatively charged, and negative charges repel each other. The crowding of negative charges in the triphosphate tail contributes to the potential energy for ATP. For ATP power, it is the release of the phosphate at the tip of the triphosphate tail that makes energy available to working cells.

Question 38

Please define metabolism, enzymes and activation energy. What effect do enzymes have on activation energy?

Answer 38

Metabolism: The total of all chemical reactions in an organism.
Enzymes: Molecules that speed up chemical reactions without being consumed by those reactions.
Activation Energy: The energy that must be invested to start a reaction because it activates the reactants and triggers the chemical reaction.
Enzymes enable metabolism to occur by reducing the amount of activation energy required to break the bonds of reactant molecules.

Question 39

Please explain the concept of ‘induced fit’ for enzymes. Define enzyme inhibitors and explain the effect that they can have on enzymes.

Answer 39

The specific molecule that an enzyme acts on is called the enzyme’s substrate. When a substrate slips into this docking station, the active site changes shape slightly to embrace the substrate and catalyze the reaction. This interaction is called induced fit because the entry of the substrate induces the enzyme to change shape slightly, making the fit between the substrate and the active site snugger.

Certain molecules called enzyme inhibitors can inhibit a metabolic reaction by binding to an enzyme and disrupting its function. Some of these inhibitors are substrate imposters that plug up the active site. Other inhibitors bind to the enzyme at a site remote from the active site, but the binding changes the enzyme’s shape. In each case, an inhibitor disrupts the enzyme by altering its shape.

Question 40

Please list and explain 3 different functions of membrane proteins.

Answer 40

Transport: A protein may provide a channel that a chemical substance can pass through.

Intercellular joining: Proteins may link adjacent cells.

Cell-cell recognition: Some proteins with chains of sugars serve as identification tags recognized by other cells.

Enzymatic activity: This protein and the one next to it are enzymes, having an active site that fits a substrate. Enzymes may form an assembly line that carries out steps of a pathway.

Cell signaling: A binding site fits the shape of a chemical messenger. The messenger may cause a change in the protein that relays the message to the inside of the cell.

Attachment to the cytoskeleton and the extracellular matrix: Such proteins help maintain cell shape and coordinate changes.

Question 41

What are the 3 main stages of cellular respiration? Please briefly explain what happens during each of these stages.

Answer 41

During glycolysis, a molecule of glucose is split into two molecules of a compound called pyruvic acid.

The citric acid cycle (also called the Krebs cycle) completes the breakdown of glucose all the way to CO2, which is then released as a waste product.

The third stage of cellular respiration is electron transport. Electrons captured from food by the NADH formed in the first two stages are stripped of their energy, a little bit at a time, until they are finally combined with oxygen to form water.

Question 42

Photosynthesis occurs in which organelle? Please describe the structure of this organelle and explain how the structure relates to its function.

Answer 42

Photosynthesis in plants and algae occurs within light-absorbing organelles called chloroplasts. A chloroplast has a double-membrane envelope. The chloroplast’s inner membrane encloses a compartment filled with stroma, a thick fluid. Suspended in the stroma are interconnected membranous sacs called thylakoids. The thylakoids are concentrated in stacks called grana. The chlorophyll molecules that capture light energy are build into the thylakoid membranes. The structure of chloroplast (with its stacks of disks) aids its function by providing a large surface area for the reactions of photosynthesis.

Question 43

Please list and explain the 3 functions of cell division.

Answer 43

Within your body, millions of cells must divide every second to replace damaged or lost cells.

Another function of cell division is growth.

All the trillions of cells in your body are the result of repeated cell divisions that began in your mother’s body with a single fertilized egg cell (reproduction).

Question 44

What type of cell division do humans use to grow and develop? What type of cell division do they use to create gametes? Why can’t humans use the same type of cell division to produce gametes as they do to grow?

Answer 44

Asexual reproduction is the creation of genetically identical offspring by a single parent, without the participation of sperm and egg. An individual that reproduces individually gives rise to a clone, a group of genetically identical individuals. In asexual reproduction, there is one simple principle of inheritance: The lone parent and each of its offspring have identical genes.

Sexual reproduction is different; it requires fertilization of an egg by a sperm. The production of gametes—egg and sperm—involves a special type of cell division called meiosis, which occurs only in reproductive organs.

Because mitosis duplicates the chromosomes as they are, and meiosis halves them, we cannot use mitosis for sexual reproduction via gametes. If we did, every generation, there would be a double of chromosomes.

Question 45

Please list and explain 3 ways that meiosis contributes to genetic variation.

Answer 45

Crossing over, the exchange of corresponding segments between nonsister chromatids of homologous chromosomes, which occurs during prophase I of meiosis.

Independent assortment at metaphase I of meiosis: the side-by-side orientation of each homologous pair of chromosomes is a matter of chance. Either or may be on the left or right.

Random segregation, is the distribution of gametes at random.

Question 46

Please list the main stages of meiosis and describe what is occurring in each of these stages.

Answer 46

Prophase I: Duplicated homologous chromosomes pair along their lengths, and crossing over occurs between homologous (nonsister) chromatids.

Metaphase I: Pairs of homologous chromosomes (rather than individual chromosomes) are aligned at the center of the cell.

Anaphase I: Sister chromatids of each chromosome stay together and go to the same pole of the cell as homologous chromosomes separate.

Telophase I: There are two haploid cells, but each chromosome still has two sister chromatids.

Meiosis II: Sister chromatids separate during anaphase II making haploid cells with non-duplicated chromosomes.